1. Field of the Invention
This invention relates to the field of security in telephony and, more particularity, to the field of allowing the secure use of DTMF tones on a telephone while the telephone is engaged in a conference call or in an environment in which the DTMF tones may be overheard, such as over the loudspeaker of a speakerphone.
2. Description of the Related Art
Standard tone-dial telephone pads utilize a standardized tone generation format called Dual Tone Multi Frequency (DTMF) to generate the familiar telephone tones to “dial” a telephone on a telephone line over a telephone network. In conventional telephones, once a handset (or headset or speakerphone) is active (either by being lifted up or by activation of a speakerphone feature), any touching of a button on the telephone's keypad will generate the DTMF tone associated with the value of the button (0-9, # or *). This tone is audible through the earpiece of the handset or headset or through the loudspeaker of the speakerphone, so that the user is made aware of the fact that the button was depressed. The DTMF tones vary, with each of the DTMF values being associated with a specific combination of frequencies, or tone.
When the buttons being depressed correspond to security numbers, such as, for example, passwords or access codes, generating a recognizable, audible, DTMF tone poses a security risk, because the other parties on the line of a conference call with the user or anyone who is within earshot of the speakerphone will hear the tones. Since the tones are standard tones, hearing the tones allows the other parties to know the buttons that were pushed, and therefore have complete possession of the security number. For example, anyone in a crowded office who uses their office speakerphone to access their bank information is giving access to their PIN number to everyone in their immediate vicinity.
In the analogous visual situation, where a password is entered manually via a keyboard, it is standard for the monitor to display an asterisk (“*”) in response to any keystroke so that anyone who can see the monitor does not see the password as it is entered. There is no known analogue to this procedure for the audio signals generated by a DTMF telephone while in the speakerphone mode. For this reason, some speakerphone manufacturers place a warning in their manuals instructing the user not to use the keypad to generate security-based DTMF tones while others can hear them.
One related, but dissimilar, technology is referred to as “ring tone muting”, in which a manual button on a telephone may activate a feature which disables the ring tone of a multi-line telephone when a user is on another line. This feature allows a user on one line of the multi-line telephone to speak on that line without being interrupted by another line ringing through. This feature is described, for example, in U.S. Pat. No. 5,191,607. This feature, however, is directed only to the ring tones of the telephone, not to the DTMF tone generated by the telephone. This feature is not directed to security and would not safeguard secret PINs, etc., as our invention proposes.
Thus, there is a need to increase the security available to users of DTMF-tone generating telephones.